Monazite sand is processed by a series of beneficiation processes to produce lighter, middle and heavier rare earth chloride fractions. The last fraction contains 55–60% Y2O3 along with Dy, Gd and Er as impurities. The preparation of 99.9–99.999% Y2O3 gains importance as it is widely used in manufacture of lasers, superconducting materials and colour T.V. Phosphors. Hence, the separation of Dy, Gd and Er is an essential prerequisite to prepare such high purity Y2O3. The three different polymerization processes described in this patent enables the separation of erbium from Y2O3.
Enantiomer Separation
Reference is made to Mark et al., WO 98/07671; 1998, who have prepared imprinted polymers for the separation of optically active compounds of ibuprofen, naproxen and ketoprofen into their respective enantiomers. Reference is made to Mosbach et al., U.S. Pat. No. 6,316,235; 2001 who have prepared magnetically susceptible components by copolymerizing one or more functional monomers and crosslinking monomer in presence of at least one imprint molecule and at least one magnetically susceptible component such as iron oxide or nickel oxide. The imprint molecule was subsequently removed to form molecular memory recognition sites. These particles are used for selective separation of two different enantiomeric forms. Reference is also made to Arnold et al., U.S. Pat. No. 5,786,427; 1998, who prepared solid phase extractant materials which include polymeric matrix containing one or more metallic complexes by molecular imprinting, which selectively binds only one enantiomer of the optically active amino acid or peptide. Reference is made to Fischer et al, U.S. Pat. No. 5,461,175; 1995 who synthesized chiral chromatographic materials for separating enantiomers of a derivative of an aryloxipropanol amine.
Sensors
Reference is made to Arnold et al., U.S. Pat. No. 6,063,637; 2000 who have developed sensors composed of a metal complex that binds the target molecule and releases a proton or includes an exchangeable ligand which is exchanged for the target molecule during the binding interaction between the metal complex and target molecule. These sensors are meant for detecting the presence of sugars and other metal binding analytes. Reference is made to Yan et al., U.S. Pat. No. 5,587,273; 1996 who prepared molecular imprinted substrate and sensors by first forming a solution comprising a solvent and (a) polymeric material capable of undergoing an addition reaction with nitrene, (b) a cross-linking agent, (c) a functional monomer and (d) an imprinting molecule.
Other Applications of Molecular Imprinting
Reference is made to Markowitz et al, U.S. Pat. No. 6,310,110; 2001 who synthesized molecular imprinted porous structures by self assembling surfactant analogue to create at least one supramolecular structure having exposed imprint groups. The imprinted porous structure is formed by adding reactive monomers to the mixture and allowing the monomers to polymerize with the supramolecular structure serving as the template. Reference is also made to Sasaki et al., U.S. Pat. No. 6,057,377; 2000 who have developed a method for molecular imprinting on the surface of a sol-gel material, solvent, an imprinting molecule to form the molecular imprinted metal oxide sol-gel materials. Reference is made to Mosbach and Olof, U.S. Pat. No. 6,255,461; 2003 who prepared artificial antibodies by molecular imprinting, wherein methacrylic acid, ethylene glycoldimethacrylate and a corticosteroid print molecule are combined to form artificial antibody. These antibodies can be used in separation and analytical procedures. Reference is also made to Magnus et al., U.S. Patent application 2003-049970; 2003 who have prepared selective adsorption material which can be used for purification or analysis of biological macromolecules.
Ion Imprinting—Anions
Reference is made to Murray, U.S. Patent Application 2003-113234; 2003 who has prepared molecularly imprinted polymer membranes for selectively collecting phosphate, nitrate and ferric ions. These membranes are prepared by copolymerizing a matrix monomer, cross linking monomer, ion imprinting complex, permeability agent and polymerization initiator, after which the ions of the ion imprinting complex and permeability agent are removed. The permeability agent creates channels in the membrane permitting membrane to communicate with the exterior surface of the the ion binding sites in the membrane. Murray, U.S. Patent Application 2003-059346; 2003 addresses the removal of phosphate/nitrate anions using selectively permeable polymer membrane. The selective binding site is prepared by ferric ion imprinting. Permeability is improved by using a polyester that associates with metal ions; the polyester is removed from the membrane by the same acid treatment used to remove ferric ion. The polyester creates channels directing the ion migration to the imprinted sites, thus, increasing the flux but maintaining selectivity.
Ion Imprinting—Cations
Reference is made to Singh et al, U.S. Pat. No. 6,248,842; 2001 who produced selective, crosslinked chelating polymers by substituting an acyclic chelating agent with a polymerizable functional group. The resulting substituted acyclic chelating agent is then complexed with the target metal ion, i.e. copper. A crosslinkable monomer is then added and the complexed material is crosslinked. The complexed metal is then removed, providing a crosslinked polymeric chelating agent that has been templated for the target metal ion. Reference is made to John et al, WO 99/15707; 1999 relating to the detection and extraction of uranyl ion by polymer imprinting wherein the complexable functionality is of the formula CTCOOH, where T is a hydrogen or any halogen (preferably chlorine), methyl and halogen substituted form thereof or COOH or PhCOOH. Gladis and Rao also teach synthesis of ion imprinted polymers for solid phase extractive preconcentration/separation of uranyl ion from host of tetravalent, tervalent and bivalent inorganic ions from both aqueous and synthetic sea water solutions. They form ternary mixed ligand complex of imprint ion with quinoline-8-ol or its dihalo derivatives and 4-vinyl pyridine in presence of styrene and divinyl benzene as functional and crosslinking monomers. Reference is made to Dai et al, U.S. Pat. No. 6,251,280; 2001 who prepared mesophorous sorbent materials by ion imprinting technique for the separation of inorganics using bifunctional ligands such as amines, thiols, carboxylic acids, sulphonic acids and phosphonic acids. Carboxylic acid groups on bifunctional ligands are used during the formation of mesophoric sorbent materials specific for erbium template ion.
Rao et al [Trends in Anal. Chem.; 2003] have reviewed the preparation of tailored materials for preconcentration/separation of metals by ion imprinted polymers for solid phase extraction (IIP-SPE). Ion imprinted polymer (IIP) materials with nanopores were prepared by formation of ternary complex of palladium imprint ion with dimethyl glyoxime and 4-vinyl pyridine and thermally copolymerizing with styrene and divinyl benzene in presence of 2,2′-azobisisobutyronitrile using cyclohexanol as porogen [Sobhi et al, Anal. Chim. Acta, 488 (2003) 173–182]. Cation imprinted SPE materials for separation of La and Gd based on diethylenetriaminepentaacetic acid (DTPA) derivatives have been prepared. Imprinting effect was observed with materials prepared in the presence of Gd salts and exhibited high efficiency and selectivity than the corresponding blank polymers [Garcia et al, Tetrahedran Lett., 39 (1998) 8651]. The functionalized monomer of DTPA was copolymerized with commercially available divinyl benzene (DVB) containing 45% ethyl styrene in presence of Gd3+ salt. The resulting IIP was found to be more selective for Gd compared to La [Vigneau et al, Anal. Chim. Acta, 435 (2001) 75]. These selective studies were extended to determine SGd/Eu and SGs/Lu using Gd imprinted IIP [Logneau et al, Chem. Lett. (2002) 202]. Biju et al [Anal. Chim. Acta, 478 (2003) 43–51] have synthesized Dy (III) IIP particles by copolymerizing styrene (functional monomer) in presence of DVB as crosslinking monomer. Some authors [Talanta, 60 (2003) 747–754] have reported improved selectivity coefficients for Dy over La, Nd, Y and Lu on post γ-irradiation of Dy IIP particles.
Molecular imprinted polymer particles prepared are widely used in separation of enantiomers, structurally related drugs, amino acid derivatives, nucleotide base derivatives etc. Thus, they find widespread use in chemical and pharmaceutical industries, water purification and waste treatment. On the other hand, the preparation of ion imprinted polymer particles are not that popular for the separation of closely related inorganic ions. The patent by Dai et al [U.S. Pat. No. 6,251,280; 2001] alone addresses this problem but is too general and do not involve separation of Er from closely related lanthanides.